An organic light emitting diode (OLED) has many advantageous features such as lightness, thinness, high color saturation and high contrast ratio, and can be applied to a flexible substrate. In recent years, OLED is extensively applied to lighting and display fields.
FIG. 1 illustrates a conventional OLED assembly 15. It includes a glass substrate 1, a first electrode layer 2, a multi-layered OLED structure 3 and a second electrode layer 4. FIG. 2 illustrates a conventional OLED light element wherein another substrate 5 is included to cover the OLED assembly 15. When the multi-layered OLED structure 3 is activated, electrons and holes are combined in the organic layer 3 to generate light. Some light emitted accordingly is reflected by the second electrode layer 4 and re-enters the organic layer 3 and then the glass substrate 1. The other passes through the first electrode layer 2 and enters the glass substrate 1. While the light is traveling out of the glass substrate 1 into the air, the total reflection phenomenon would occur in the interface. In general, the total reflection phenomenon comes up when the light travels from a high refractive index medium into a low refractive index medium such as air. Thus the amount of light is reduced. Generally, the external out-coupling efficiency of the OLED assembly 15 is only about 10% to 20%. How to improve the out-coupling efficiency is a serious issue.
Furthermore, as shown in FIG. 2, the size of the lower base substrate 1 is larger than that of the upper cover substrate 5. Therefore, the exposed portion 13 of the lower base substrate is likely to crack during assembling, conveying or using. How to prevent the OLED glass substrate from crack is also an important issue.